i have an M880 and the ammeter was doing the same, the lights also flickered but i didn't worry about that as every old mopar i've had has done that. I also noticed the light to illuminate my auto meter fuel gauge would flicker just like the other stuff. My alternator died so I put another on and I still had the flicker in the lights. I think I also replaced the voltage regulator. Didn't help.
I figured out that my bulkhead connection was pretty bad so i bypassed that, put a voltage gauge on and converted to the Denso style alternator. The light in the fuel gauge doesn't flicker now...i actually left the ammeter in the truck but it's doesn't do anything now the way the alt output is wired up.
